Published 5:30 am, Sunday, April 27, 2008

Neil Shubin, a paleontologist at the University of Chicago and the Field Museum in Chicago, wrote Your Inner Fish, which investigates the evolution of bodily quirks.

Neil Shubin, a paleontologist at the University of Chicago and the Field Museum in Chicago, wrote Your Inner Fish, which investigates the evolution of bodily quirks.

Photo: JOHN WEINSTEIN, THE FIELD MUSEUM

Story of evolution can be seen as comedy of errors

1 / 1

Back to Gallery

PHILADELPHIA — "Oh what a piece of work is man," wrote Shakespeare, long before Darwin suggested just how little work went into us. Somehow, that same process that gave us reason, language and art also left us with hernias, flatulence and hiccups.

One argument scientists often make against so-called intelligent design — the idea that evolution cannot by itself explain life — is that on closer inspection, we look like we've been put together by someone who didn't read the manual, or at least did a somewhat sloppy job of things.

Viewed as products of evolution, however, our anatomical quirks start to make sense, says University of Chicago fossil hunter and anatomy professor Neil Shubin, author of the recent book Your Inner Fish. And by focusing on our less lofty traits, evolutionary biology can help dispel one of the most egregious and even tragic fallacies surrounding Darwinian evolution — that it moves toward perfection, with man at the apex of some towering ladder.

Evolution of hiccups

That misreading of evolution has been connected to the eugenics movement of the early 20th century, with the Nazis extending the man-as-ideal notion to blue-eyed blond German-man-as-ideal notion.

"Darwin didn't believe it, but some, who saw it through a more religious light, tended to want to interpret evolution as a steady march toward the pinnacle of humanity," says University of Pennsylvania ethicist Art Caplan, who has written extensively on the eugenics movement.

By today's understanding, evolution by natural selection doesn't march toward anything — it just modifies existing creatures to better compete in ever-shifting environments.

Understanding something as seemingly trivial as the evolution of hiccups can help clear up some profound misperceptions on the nature of life and humanity.

The sound of a hiccup echoes back to our very distant past as fish and amphibians some 375 million years ago, says Shubin. It's really just a spasm that causes a sharp intake of breath followed by a quick partial closing of our upper airway with that flap of skin known as the glottis. It's best if you can nip it in the first couple of hics, he says.

It's much harder to stop once you've let yourself get up to 10. By that point you've reverted to an ancient breathing pattern orchestrated by the brain stem that once helped amphibians breath, letting water pass the gills without leaking into the lungs.

"Tadpoles normally breathe with something like a hiccup," Shubin says.

The theme of his book is that we owe much of our anatomy to our animal ancestors. "Parts that evolved in one setting are now jury-rigged to work in another," he says. "When you look at the human body, you see layer after layer of history inside of us."

The first layer is what we share with chimpanzees and gorillas. The next goes back to mice and cows, while further down, you get to the relatively underappreciated layers we share with fish — which include the backbone and basic layout of the body.

Fishy news about hernias

Our descent from fish explains why men are so much more prone to hernias than women. In fish, Shubin explains, the testicles lie up near the heart.

(Had they remained there, he said, it would give a whole new meaning to the Pledge of Allegiance.)

The budding gonads still form up high in a human embryo, but male mammals reproduce better with their sperm kept a bit cooler than body temperature. And so during gestation, human testicles take an incredible journey down through the body to their destination in the scrotum.

The trip downward puts a loop in the cord that connects the testes to the penis, leaving a weakness in the body wall where the cord attaches that never quite repairs itself.

Hence the trouble with hernias down the road.

The matter of milk

No good story about human design flaws can pass up a discussion of flatulence — and science has addressed the kind that would occur if everyone in the world drank a tall glass of milk at the same time.

From genetic studies it appears that so-called lactose intolerance was our ancestral state.

A few people, however, were genetically gifted with an enzyme called lactase, which breaks down lactose, and in groups that started drinking lots of milk around 10,000 years ago, that version of the gene started to take over.

Scientists recently sequenced the lactase gene and found 43 different variations that allow adults to drink the milk of other animals.

"It's the first clear evidence of convergent evolution," Patel said, though it's not known whether those lacking this innovation failed to pass on their genes because they suffered from lack of nutrition or just didn't get invited to any parties.